Double acting two stroke cycle internal combustion engine



A. E. BRCWN Dec. 22, 1959 DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE 3 Sheets-Sheet 1 INVENTOR.

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B ABAI B Filed Feb. 6, 1957 Dec. 22, 1959 DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE A. E. BROWN Filed Feb. 6, 195? 3 Sheets-Sheet 2 3 3 30 3 32 FIG.]I g 43 4 l g 42 II N [El U E \l H 1 l\ 5; t 27 I 2 38 258 g i 1 4 I: i 439 1 I3 44 g 7= \l l I I I II 29 1M 4612/ 4 i 4: 2 5 %E E 28 45 I H I N III m H g: I X INVENTOR N m y Eg k a 35/] I/V/ I U Dec. 22, 1959 A. E. BROWN 2,918,045

DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE Filed Feb. 6, 1957 3 Sheets-Sheet 3 III INVENTOR w/ 4? W 7 An //K/// A l l United. States Patent DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE Arthur E. Brown, Nahant, Mass.

Application February 6, 1957, Serial No. 638,579

Claims. (Cl. 123-62) A general object of the invention is to provide an engine that is light in weight and compact in overall size for a given power output. The engine would have its best applications in powering boats, chain saws, portable fire pumps, portable electric plants, drone planes, small helicopters, and other applications where light weight and compact size are important.

Another object is to improve the thermal efficiency by employing uniflow type scavenging in place of cross flow or loop scavenging. The flow of scavenging air through each working chamber is substantially unidirectional and this reduces eddy currents and short circuiting. In conventional carburetor type cross scavenge and loop scavenge engines a large portion of the inlet flow is short circuited to the exhaust port so that unburned carbureted fuel is lost out the exhaust port. This is the principal reason why cross scavenged carburetor engines show a poor thermal efficiency compared with four cycle engines.

Another object is to provide an engine which is simple in construction. This object is attained because the engine is double acting and has uniflow scavenging, yet, it does not require complicated cam operated poppet valves in each end of the working cylinder. Instead, the valving is accomplished with valve pistons attached to the working piston. The engine is also simple in construction since it is double acting, yet it does not require a cross head, cross head guide, piston rod, or stuffing box.

In conventional engines (such as might be used in an outboard boat motor, for example) it is customary to employ two small cylinders instead of a single large cylinder in order to obtain an engine of given displacement and power output. The reason for this is that it gives a smoother flow of power with two smaller impulses per revolution instead of a single large impulse. An advantage of this invention is that the working piston is double acting and therefore has two power strokes per revolution. This means that the single crank engine shown in Fig. I can take the place of a double crank two cylinder single acting engine.

Another advantage of the engine is that it is well suited to operate at high speed because it is two cycle double acting and therefore the inertia forces of the reciprocating parts are opposed at each end of each stroke by a gas pressure force on the working piston. This means that the bearings are not subjected to high reciprocating forces during high speed operation. Also, the engine is well suited to operate at high speed because of unifiow scavenging and free breathing characteristics. The exhaust ports are located around the full periphery of the cylinder in stead of just a portion ofthe periphery (as in cross scanvenged engines) and this means less flow resistance for the exhaust gas. With unifiow scavenging, the gases rflow through a single path the length of the cylinder. This requires less time than cross flow scavenging where the gases must flow from bottom to top and return.

Another object is to make the engine self-scavenging without the need-ofan additional scavenge pump such as a Roots blower or reciprocating pump pistons.

Another advantage is that the double acting working piston is cooled by the flow of inlet air through its center.

Another object is to provide means for pump scavenging during starting and slow speed operation of the engine.

The engine is light in weight and compact in overall size because: (1) it is double acting; (2) the working cylinder is closely connected to the crankcase without the need of a cross head, cross head guide, piston rod, or I stufling box; (3) it is well suited to operate at high speed; (4) it has a higher mean effective pressure because of unitlow scavenging in place of cross flow scavenging; and

(5) it is self scavenging without the need of an additional scavenging pump.

As an indication of compactness, the single crank engine shown in Fig. I is drawn full scale within a 6 X 11 /2 inch border (excluding carburetor) and has a displacement volume of 21 cubic inches.

Fig. I is a sectional view of one form of the engine in which both valve pistons 9 and 10 serve as scavenge pumps for scavenging both working chambers 5 and 6 during starting and low speed operation of the engine.

Fig. II is a sectional view of another form in which the displacement volume of the valve pistons 27 and 28 is substantially equal to the displacement volume of the working piston 29.

Fig. III is another form in which all the fuel-air mixture is supplied to the crankcase.

Referring to Fig. I, the working cylinder 1 is fastened to the crankcase 2 which encloses the crankshaft 3. The double acting working piston 4 is reciprocable in the working cylinder. A front working chamber 5 and a back working chamber 6 are located in the working cylinder. Throughout the following description and claims, the front of the engine is referred to as the end nearest the crankshaft. The front valve cylinder 7 and back valve cylinder 8 are fastened to the front and back ends respectively of the working cylinder. A front valve piston 9 and a back valve piston 10 are fastened integrally to the working piston. A connecting rod 11 connects the piston pin 12 to the crankshaft. Passages 13 are for liquid cooling. Spark plugs 14 are for ignition.

The engine in Fig. I operates as follows: Upward motion of the pistons draws a fuel-air mixture (from a carburetor not shown) through the opening 15, through the reed valves 16, and into the crankcase 2. Downward motion compresses the mixture in the crankcase. Near bottom dead center, the ports 17 overlap the back inlet ports 18 and the compressed mixture flows into the back working chamber 6. The working piston uncovers the exhaust ports 19 and the exhaust gas passes out of the chamber 6 with a unifiow type scavenging operation. Further rotation of the crankshaft compresses and fires the mixture in the back working chamber 6.

Downward motion or" the pistons draws a fuel-air mixture up through the conduit 20 (rectangular in cross section), through reed valves 21, and into the back valve cylinder 8. Upward motion compresses the mixture in the cylinder 8. Near top dead center, the ports 17 (in the wall of the back valve piston) are in communication with the recessed slots 22. The compressed mixture then flows through the slots 22, through ports 17, through the hollow passage 23, through front inlet ports 24, and into the front working chamber 5. The working piston 4 uncovers the exhaust ports 19 and the exhaust gas passes out of the working chamber 5 with a unifiow scavenging operation. Further rotation of the crankshaft compresses and fires the mixture in the front working chamber 5.

It is noted that the two valve pistons 9 and 10 serve (in addition to their function as valves) as scavenge pumps for supplying scavenging air to the working chambers.

Patented Dec. 22, 1959 I 3 The displacement volume of the valve pistons 9 and 10 is substantially less than that of the working piston 4. This means that the working chambers 5 and 6 do not receive a full fresh charge from the valve pistons 9 and 10, but this is satisfactory for starting and low speed operation of the engine.

Scavenging of the front working chamber 5 during high speed operation of the engine will next be explained. The exhaust ports 19 are made longer than the inlet ports 24 so that the exhaust ports are partly uncovered before the inlet ports start toopen. This period is known as the exhaust lead. As the exhaust ports begin. to open, the pressure of the exhaust gas in the working chamber is still above atmospheric due to yet incomplete expansion. A rapid opening of the exhaust ports causes the exhaust gases to rush out at high velocity because of the pressure difference just mentioned. The inertia of the outrushing exhaust gas causes a partial vacuum in the working chamber 5 so that a fresh charge is then drawn inthrough the inlet ports 24.

The back working chamber 6 is scavenged during high speed operation of the engine in a similar manner and the.fresh charge is drawn in through the inlet ports 17 because of the inertia effect of the exhaust gas.

The basic principle of using the inertia of an outrushing mass of exhaust gas to draw a fresh charge into an engine cylinder is known as the Kadenacy effect. Gas inertia or Kadenacy type scavenging is particularly well suited for this type engine because the Whole circumference of the working cylinder is available for making a large exhaust port and also because of the uniflow scavenging action.

Some form of seal rings are required to seal the valve pistons in their cylinders. Expanding type seal rings 25 on" the back valve piston and contracting seal rings 26 in-the front valve cylinder are employed in Fig. I since this combination results in a much shorter overall length engine than do other sealing arrangements.

The engine shown in Fig. II is similar to that in Fig. I except that the displacement volume of the two valve pistons 27 and 28 is made approximately equal to that of the working piston 29. This means that the two valve pistons pump most of the fresh charge to the working chambers. This feature makes the engine less compact but'permits a more positive scavenging when operating over a'wide speed range.

The pressure. responsive reed valves 30 are located around the outer periphery of the back valve cylinder so as to reduce the overall height of the engine. The valves shown employ a cylindrical valve seat surface 31 and curved reeds 30 which seat over the valve ports 32. The rigid ring 33 prevents the curved reeds 30 from deflecting too far radially inward.

The engine shown in Fig. II operates as follows: Upward motion of the pistons draws a fuel-air mixture through the inlet 34, through the reed valves 35, and into the crankcase 36. Downward motion compresses the mixture in the crankcase. When the pistons near bottom 'deadcenten'the ports 37 come into communication with the back inlet ports 38 and the compressed fuel air mixture flows into the back working chamber 39. The working piston uncovers the exhaust ports 40 and the exhaust gas passes out of the working chamber 39 with a uniflow scavenging action.

Downward motion of the pistons draws a fuel-air mixture up the conduit 41, through the reed valves 30, and into the back valve cylinder 42. On the upstroke of the pistons, the reed valves 30 close and the fuel-air mixture is compressed in theback valve cylinder. As the pisto'ns approach top dead center, the ports 37 come in communication with the slots 43 in the cylinder wall and the compressed mixture flows through the ports 37 and into to the front working chamber 46. The working piston 29 uncovers the exhaust ports40, and the exhaust gas passes out of the front working chamber 46 with a unifiow type scavenging action.

Fig. III illustrates another form of the invention in which valve piston sealing is accomplished with expanding type piston rings 59 and 60 on each valve piston. The cylinder heads are providedjwith recesses 61 and 62 which serve as inlet ports. The back valve piston 63 is provided with a closed end cap 64. The engine is started and operated as follows: Upward motion of the pistons draws a fuel-air mixture through the reed valves 65 into the crankcase 66. The reed valves 65 then close and the fuel-air mixture in the crankcase is compressed during downward motion of the pistons. Near bottom dead center, the ports 67 (in the wall of the back valve piston) come in communication with the back inlet ports 62. The compressed mixture then flows up through the hollow passage 68, through ports 67 and 62 and into the backworking chamber 69. The working piston 70 'uncovers the exhaust ports 71 andthe working chamber 69 is scavenged witha 'uniflow scavenging operation. During high speed operation, both working chambers 69 and. 72 are scavenged by means of the. gas inertia or Kadena-. cy principle. During high speed operation, the vacuunr caused by the inertia of the outrushing mass of exhaust gas draws the fuel-air mixture through reed valves 65 and the inlet ports 61 and 62 into both working chambers 72 and 69.

It will be obvious to those skilled in the art that various modifications are possible and I do not-desire to be, limited by the disclosure as given for purposes of illustration, but only to the scope of the appended claims.

What is claimed is:

1. The combination in a double acting two stroke cycle internal combustion engine of a crankcase, a crankshaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a double acting working piston reciprocable in said working cylinder, a front valve cyl? inder and a back valve cylinder fastened to the front and back ends respectively of said working cylinder, a front valve piston and a back valve piston reciprocable in their respective valve cylinders, said three pistons being fastened together so as to'form a reciprocating piston assembly, a connecting rod connecting saidpiston r assembly to said crankshaft, said working cylinder having exhaustportscontrolled by said working piston, said;

working cylinder having an'annular front Working chamber and an annularback working chamber inside it, said front working chamber having front inlet ports for the introduction of air, said front inlet ports being controlled by said front valve piston, said back Working chamber having backinletports for the introduction of air, said back inlet ports being controlled by said back valve piston, each working chamber having a uni-flow type scavenging operation exhausting through said exhaust ports, said front valve cylinder being in open communication with the interior of said crankcase, said-three pistons having a hollow passage opening into the interior of said crankcase, a crankcase valve adapted to admit air to the interior of the crankcase during the upstroke of said pistons, said crankcase valve preventing the escape of air being compressed in-the crankcase during the downstroke of the pistons, said back valve piston having a closed end cap and ports in its wall, said ports in thewall of the back valve.piston communicating with said back inlet ports when the pistons are at bot-tom dead center, said hollow passage serving to conduct compressed 2 111s Qm in t oitin a doub e-act g woxstmks was:

internal combustion engine of a crankcase, a crankshaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a double acting working piston reciprocable in said working cylinder, a front valve cylinder and a back valve cylinder fastened to the front and back ends respectively of said working cylinder, a front valve piston and a back valve piston reciprocable in their respective valve cylinders, said three pistons being fastened together so as to form a reciprocating piston assembly, a connecting rod connecting said piston assembly to said crankshaft, said working cylinder having exhaust ports controlled by said working piston, said working cylinder having an annular front working chamber and an annular back working chamber inside it, said front valve cylinder having front inlet ports for the introduction of air into said front working chamber, said front inlet ports being controlled by said front valve piston, said back valve cylinder having back inlet ports for the introduction of air into said back working chamber, said back inlet ports being controlled by said back valve piston, each working chamber having a uniflow type scavenging operation exhausting through said exhaust ports, said front valve cylinder being in open communication with the interior of said crankcase, said three pistons having a hollow passage in open communication with the interior of said crankcase, a crankcase valve adapted to admit air tothe interior of the crankcase during the upstroke of said pistons, said crankcase valve preventing the escape of air being compressed in the crankcase during the downstroke of the pistons, said back valve piston having a closed end cap and ports in its wall, said ports in the wall of the back valve piston communicating with said back inlet ports when the pistons are at bottom dead center, said hollow passage serving to conduct compressed air from the crankcase to said back inlet ports so as to scavenge the back working chamber, a pressure responsive valve adapted to admit air into said back valve cylinder, and said end cap being adapted to compress air in said back valve cylinder so that when the pistons are at top dead center the compressed air fiows through ports in the wall of the back valve piston and then flows through said hollow passage- Way and then flows through said front inlet ports and into the front working chamber.

3. The combination recited in claim 2 wherein a piston pin joins said connecting rod to said piston assembly, and wherein said piston pin intersects said hollow passage in the pistons, and wherein said piston pin is located such that it is within said working cylinder when the pistons are at top dead center.

4. The combination recited in claim 2 wherein an external conduit is provided for supplying a fuel-air mixture to both the crankcase and the back valve cylinder from a single source.

5. The combination in a double acting two stroke cycle internal combustion engine of a crankcase, a crank shaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a double acting working piston reciprocable in said working cylinder, a front valve cylinder and a back valve cylinder fastened to said working cylinder, a front valve piston and a back valve piston reciprocable in their respective valve cylinders, said three pistons being fastened together so as to form a reciprocating piston assembly, a connecting rod connecting said piston assembly to said crankshaft, said working cylinder having exhaust ports controlled by said working piston, said working cylinder having an annular front working chamber and an annular back working chamber inside it, said front valve cylinder having front inlet ports for the introduction of air into said front working chamber, said front inlet ports being controlled by said front valve piston, said back valve cylinder having back inlet ports for the introduction of air into said back working chamber, said back inlet ports being controlled by said back valve piston, each working chamber having a uniflow type scavenging operation exhausting through said exhaust ports, the combined displacement volume of said valve pistons being substantially less than the total displacement volume of said working piston, at least one of said pistons serving as a scavenge pump for supplying air to one of said working chambers during starting and low speed operation of said engine, and said working chambers being scavenged by means of gas inertia during high speed operation of said engine.

References Cited in the file of this patent UNITED STATES PATENTS 288,396 Baldwin Nov. 13, 1883 886,846 Nicoll May 5, 1908 1,099,860 Pratt June 9, 1914 1,175,017 Seymour Mar. 14, 1916 2,102,559 Kadenacy Dec. 14, 1937 2,123,569 Kadenacy July 12, 1938 2,256,437 Kylen Sept. 16, 1941 2,780,208 Brown Feb. 5, 1957 

